The molding of a composite material with a thermoplastic or thermosetting matrix from prepreg plies requires an operation to cure/consolidate the preform made up of the layered structure of said plies. That curing/consolidating operation is generally carried out in an autoclave, that is to say in a large fully closed enclosure with a heating system and a pressurizing system, where the layered structure is bagged and a vacuum is applied to it. In particular, such an autoclave makes it possible to obtain uniform temperature in the layered structure during the curing/consolidating operation. An autoclave is a piece of production equipment with a high cost, and, particularly when it is adapted for making large parts, is a unique resource within a production system, the availability of which determines production management. The price of an autoclave is exponentially proportional with its diameter and with the cost of the door to the inside of the autoclave, which must be sealed when it is subjected to pressure and a large temperature difference between its inner and outer faces. Thus, the more an autoclave is capable of working with large parts at high temperature, the higher its cost. In order to avoid the constraints imposed by the availability and cost of such a piece of equipment, particularly for working with composite materials with organic matrices, methods known as out-of-autoclave methods are used particularly for curing or consolidating parts made of such materials. These out-of-autoclave methods use independently heated molds or molds that can be placed in a stove and means for increasing the pressure inside the mold.
Typically, out-of-autoclave methods for working with a composite material with fiber reinforcement in thermosetting resin are methods that use resin injection, by transfer or infusion, where vacuum is applied to the mold cavity, before the process or otherwise. The most conventional methods initially involve laying up plies of dry fibers, inserted in the closed cavity of a mold, and liquid resin is injected under pressure in said cavity. The mold used for these methods is a rigid closed mold that defines a cavity between two parts, which mold is designed to withstand the pressure inside said cavity and the corresponding closing force. The preform made of dry fibers is located in the cavity between the molding faces of the two rigid parts. That is true, for example of the RTM (Resin Transfer Molding) method.
These out-of-autoclave methods include vacuum-assisted methods such as the LRIVAP or Liquid Resin Injection Vacuum Assisted Process method or the VARTM or Vacuum Assisted Resin Transfer Molding method, which use tooling known as soft tooling, in which a layered structure of dry fibers is laid up on a molding face of said tooling. Said layered structure is bagged and a vacuum is applied to it before the resin is injected.
When these out-of-autoclave methods are used according to the prior art for large parts such as, as non-limitative examples, parts of the wing or fuselage of an aircraft or a wind turbine blade, uniformly heating the cavity of the mold or the matrix in which the layered structure is located is tricky. In the case of a mold with two faces defining a closed cavity, the mass of the mold is large and requires a lot of energy. The use of a mold with a single molding face makes it possible to reduce the mass of the molding device, but only to some extent, because the reduction of thermal inertia becomes a handicap for obtaining uniform temperature. Further, it is difficult to insert a device for heating by fluid circulation or by electrical resistance into a lightweight mold without increasing the sections of the mold. The lack of uniformity of the temperature is also liable to produce distortions in the shape of the mold, in addition to its influence on the flow of resin. Thus, these methods, particularly when used for large parts, are not suitable for application with an independent mold, and are commonly applied in a stove. While such stoves represent a smaller investment than that required for an autoclave, they do however pose the problem of their availability and require heating a fully closed volume that is larger than that made up of the cavity of the mold or the layered structure.
The document EP1 894 442 describes a method for heating a molding surface using inductors inserted in cavities, grooves or bores, machined in a mold. The thickness of the material located between said cavities and the molding surface is used to make the temperature of the molding surface uniform during heating resulting from the circulation of alternating current in said inductors. Thus, this type of tooling, which is satisfactory with medium-sized parts such as the hoods of automotive vehicles, requires a carcass that is relatively massive and turns out to be expensive with very large parts such as those for which the invention is intended.
The document EP 1 728 411/U.S. Pat. No. 7,679,036 describes a device and a method for processing material contained in a cavity, particularly a sealed cavity, comprising two half molds that are electrically conductive placed opposite each other, where the opposite faces of the two half molds which demarcate the cavity are electrically insulated from each other, and are made of magnetic material. The two half molds are surrounded by the coils of an induction circuit. The gap created between the two half molds makes it possible to make induced currents circulate on the faces of the cavity and thus obtain heating focused on those faces without integrating heating means in the half molds such as an electrical resistor, a fluid (vapor or oil) circulation circuit or inductors. In that example of the prior art, the induction circuit is configured in two separable parts, joined to each of the half molds and connected mechanically and electrically when said half molds are brought closer in order to close the cavity. Thus, this device of the prior art is particularly designed to be used in combination with a means to open and close the mold, such as a press.